Moving image encoding schemes such as MotionJPEG, MPEG, and the like have been established. Vendors have developed, using these encoding schemes, image sensing apparatuses such as digital still cameras, digital video cameras, and the like, moving image viewers, and DVD recorders, which have been put into practical use, and a personal computer (to be referred to as a PC hereinafter) and DVD player allow easy playback.
JPEG2000 has been standardized as an encoding scheme recently. One of the specifications of JPEG2000 is Motion-JPEG2000 that can handle a high-resolution moving image, and has received a lot of attention as the next generation moving image compression encoding scheme (for example, ISO/IEC-15444-3: JPEG2000 standard part-3, etc.).
Nowadays, moving images are handled in various forms by the aforementioned apparatuses. A moving image is recorded as an analog signal or digital data in some cases. When a moving image is an analog signal, an NTSC monitor is often used to display a playback image. On the other hand, when a moving image is digital data, its playback image is often displayed on a display having a plurality of vertical display frequencies such as a display connected to a PC.
As a moving image playback method, high-speed playback that starts playback after a desired image is found is known. As a method of playing back and displaying an analog moving image signal on an NTSC monitor at high speed, a method of making a magnetic tape as a recording medium travel at high speed, and simultaneously displaying a plurality of pieces of video information with a time difference, which are played back from a plurality of recording tracks, is available. Also, as a method of playing back and displaying digital moving image data at high speed, a method of making playback while skipping frames at predetermined intervals is known. Furthermore, a method of dividing each frame that forms digital moving image data, compositing one frame for a plurality of frames as a high-speed playback image, and playing back and displaying that image at high speed like an analog moving image is known (e.g., Japanese Patent Laid-Open No. 8-163494).
On the other hand, as users have more chances to handle moving images, their requirements are increasing. To meet such requirements, vendors provide various value-added products.
For example, the vendors of digital still cameras and digital video camera add a liquid crystal display that allows the user to confirm a video picture sensed by himself or herself at that place. A video picture displayed on this display includes not only a normal playback image but also a special playback image, enlarged/reduced-scale image, and the like. For this reason, the user can appreciate the sensed video pictures by various methods, and can sufficiently enjoy acquired video pictures even on a digital still camera or camcorder.
A moving image is often played back at high speed. For example, double-speed playback will be examined below. In this case, two different types of processes may be used.
In one process, if the normal playback speed is 30 fps (frames/sec), a moving image is played back at 60 fps in the double-speed playback mode. In the other process, only one of two frames is played back.
In the former process, the load on a decoding process substantially becomes twice that for a normal speed. In case of hardware implementation, a high-speed clock signal or a large circuit scale is required, and power consumption increases. In case of software implementation, a CPU which can sufficiently follow that speed is required. In the latter process, since frames are decimated, a moving image is played back awkwardly.